1. Field of the Invention
The present invention relates to an antenna device and, more particularly, to an antenna device comprising an antenna body including a conductor, an equivalent circuit of said conductor comprising an inductive component and a resistive component in a series connection. The antenna device is used for a mobile communication apparatus such as a mobile telephone and a pager.
2. Related Art of the Invention
Generally, bandwidth x gain=constant if the volume of an antenna remains constant, and an antenna having a increased volume or a plurality of antennas having different resonant frequencies are used to expand the bandwidth with the gain maintained so that the antenna works with a mobile communication apparatus which requires a wide band for accommodating transmission and reception frequencies therewithin. The former case is represented by a 10 cm whip antenna, 5/8 times the wavelength of a reception frequency or the wavelength of a transmission frequency in the system of PDC (Personal Digital Cellular) 800, one type of portable telephone, having a reception frequency of about 818 MHz, a transmission frequency of about 948 MHz, a bandwidth of 16 MHz for each of transmission and reception. The latter case is represented by a receiving loop antenna 61 and a transmitting inverted F antenna 62, both, mounted on a board 63 as shown in FIG. 15 in a duplex pager system having a reception frequency of about 940 MHz, a transmission frequency of about 901.5 MHz and a bandwidth of 1 MHz for each of transmission and reception.
However, if the bandwidth of the above conventional antenna is widened to transmit and receive on frequencies in a wide range for use in a mobile communication apparatus, the volume of the antenna has to be increased, a plurality of antennas having different resonant frequencies have to be mounted on a circuit board, and as a result, the antenna occupies a wide area in the mobile communication apparatus. This presents difficulty implementing compact design in the mobile communication apparatus.